AIP - 96: Adjust savings rate update methodology

Hello, This is a proposal to update the operational way with which the rates in Angle savings product (stEUR and stUSD) are updated. ## Context The way rates for stEUR and stUSD are currently computed is explained in details [here](https://docs.angle.money/savings/savings). Precisely speaking, they are updated on all the chains where the contracts are deployed by the guardian multisig when the following conditions are met: - last rate update was 7 days ago - or, current rate is too high and...